Comprehensive Design And Implementation Of Short-wave Multi-channel Modulation And Channel Simulation Function

In the research of short-wave communication systems,it is necessary to test the developed communication equipment.If tested on the actual communication link,it will cost a lot.If testing with experiment devices,the environment with special equipment including baseband channel simulator or the RF channel simulator,needs to be built,which takes a lot of time and effort.If the channel simulation function is added to the baseband transmission unit of the short-wave communication system,the developer can set different channel conditions for testing whenever and wherever necessary,which greatly reduces the development cost and period,and has strong practical value.Therefore,based on the needs of scientific research project,a comprehensive processing unit of short-wave multi-channel modulation and channel simulation function is developed in this thesis.Firstly,a short-wave multi-channel vocoder data transmission system scheme based on 3kHz bandwidth is proposed in this thesis.The data frame structure of transmission waveform,shaping filtering and modulation technology are discussed in detail.The LDPC(Low Density Parity Check)code used is introduced,and the output waveform of the transmitter is simulated by Matlab.Secondly,the channel propagation characteristics of short-wave are analyzed and discussed,including the causes of multipath effects,fading,Doppler frequency shift,radio interference,etc.and their effects on short-wave communication.Two classic short-wave channel models: Watterson narrowband model and ITS broadband model are introduced and analyzed,and the design specifications of the channel simulation are given.According to the Watterson channel model,a channel model framework that meets the requirements is comprehensively designed.Two realization algorithms of fading are analyzed: the sine wave superposition method and the shaping filter method,and two multi-channel noise generation algorithms: filtering method and spectrum shifting method are given.In addition,the signal processing implementation algorithms such as Doppler frequency shift and multipath delay are also introduced.Finally,a four-channel transmission unit is designed and implemented on a hardware platform based on DSP(Digital Signal Processing),including modulated signal generation module and channel simulation processing module.When the modulated signal is output,different and independent channel conditions can be added,including frequency shift,multipath delay,fading and noise.In this way,four signals with different channel conditions are output through four D/A(Digital-to-Analog converter),which can be further sent to diversity merge unit for next processing.